Hydraulic fracturing is the parting of a desired section of an oil or gas bearing formation by the application of hydraulic pressure. The fracture made in this manner may be extended from the well bore by continued pumping. The extending distance depends on several factors such as injection rate, formation characteristics and fracturing fluid properties. Selected particles, added to the fracturing fluid, are transported into the fracture. These act as propping agents to hold the fracture open when the applied pressure is dissipated, thus leaving a channel of high flow capacity connected to the well bore. Because of the above-mentioned factors, in some wells it is necessary to use higher than usual pressure to accomplish satisfactory fracturing. Due to a high pressure loss in fracturing through tubing or "down tubing", it is necessary to fracture through the casing or "down casing" in such wells. As will be described more fully hereinafter, previous practice was to put a single joint of tubing down to a tubing spool to protect blowout preventors from the above mentioned selected particles and then pass fracturing fluid through this joint of tubing and into the well casing in order to fracture down casing. High costs were incurred when taking that joint of tubing out of the well under high well pressure and then putting a packer down casing either with tubing or with a wireline to secure the fracturing fluid in the well and release well pressure above the packer.
Accordingly, the present invention seeks to overcome the above and other problems in connection with high pressure fracturing as more particularly described hereinafter.